Magnetic resonance imaging techniques are currently used to obtain images of various portions of an anatomical region of interest. A magnetic resonance imaging magnet assembly generates magnetic field gradients to spatially encode the nuclear magnetic resonance (NMR) signals from an anatomical region which is positioned in the path of the field gradients. The NMR signals are detected and then processed to obtain images that provide an accurate representation of anatomical features and soft tissue contrast of the region of interest.
Early magnet assemblies for performing magnetic resonance imaging on a patient required that the patient be positioned in a narrow, substantially enclosed gap region. These magnet assemblies induced claustrophobic reactions in the patient and also prevented another person, such as a medical attendant or physician, from having easy access to the patient while a region of the patient was scanned to obtain a magnetic resonance image.
Recently, open type magnetic resonance imaging magnet assemblies have been developed. These open assemblies have a large gap region for receiving a patient, are configured to be less confining and also permit greater access to the patient during scanning. For example, magnet assemblies with open areas on four sides of the patient, such as those described in U.S. Pat. No. 6,023,165, filed on Dec. 18, 1992 and issued on Feb. 8, 2000, and U.S. Pat. No. 6,201,394 B1, filed on Nov. 21, 1997 and issued on Mar. 13, 2001, both assigned to the assignee of the present invention and incorporated by reference herein, have been proposed which provide for imaging volumes large enough to conduct surgery therein.
U.S. Pat. No. 6,023,165 also discloses magnet assemblies configured in the form of a room with only the polar regions of the magnet visible in the room, such as projecting from either the horizontal or vertical walls of the room. These magnet assemblies further reduce claustrophobic stress for the patient and allow others even greater access to the patient during scanning. In particular, these magnet assemblies provide that one or more persons can have access to the patient while the patient is positioned between the poles of the magnet assembly during scanning. This accessibility enables a physician to perform surgical procedures on the patient that are guided by the images obtained from scanning a desired anatomical region of the patient. The images obtained using open magnet assemblies, however, may not necessarily have sufficient resolution to be useful for guiding surgery in an anatomical region, which generally is smaller than the anatomical region that the magnet assembly is scanning.
Therefore, there exists a need for an open magnet assembly for magnetic resonance imaging which allows several persons to have access to a patient while the patient is undergoing scanning and furthermore provides a capability of increasing the resolution of scanning over a more limited region of interest of the patient, as desired, simply and conveniently while maintaining access to the patient substantially unimpeded and without requiring that the patient be moved.